We take in a lot of things in our body the whole day. They need to be simultaneously excreted out of the body to maintain the body’s steady state. This process of removal of chemical wastes from our body is known as excretion. There are a number of substances that our body needs to get rid of. Some of them are carbon dioxide, nitrogenous wastes, excessive salts and vitamins, water and bile pigments. Excretion in humans occurs through the kidney, sweat glands, lungs etc.
Kidneys are the chief excretory organs and are mainly concerned with the excretion of urea in the form of urine. The function of our kidney is monitored and regulated by the feedback mechanisms which involve hypothalamus, juxtaglomerular apparatus, and the heat.
Regulation of Kidney Function
When there is excessive loss of fluid from the body, osmoreceptors are activated which stimulate the hypothalamus to release ADH – antidiuretic hormone from neurohypophysis. This hormone helps in reabsorption of water from the latter parts of the tubule and prevents the loss of water from the body. When the fluid volume of body increases, osmoreceptors are switched off and the release of ADH is suppressed. ADH may also increase the blood pressure thereby increasing the glomerular blood flow. When the glomerular blood flow decreases, juxtaglomerular cells release renin which converts angiotensin in blood to angiotensin I which is further converted to angiotensin II. This causes an increase in glomerular blood pressure. It converts angiotensin in blood to angiotensin I. It is further converted to angiotensin II. This causes an increase in glomerular blood pressure.
Another function of angiotensin II is activation of the adrenal cortex to release aldosterone which causes reabsorption of sodium ion and water from the distal parts of the tubule. This also leads to an increase in blood pressure and glomerular filtration rate. This entire mechanism is known as the renin-angiotensin mechanism. The atrial Natriuretic factor is released when there is an increase in blood flow to the atria of the heart. It can cause a decrease in blood pressure by dilating blood vessels.
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